Alumina-coated silica nanoparticles (NPs) grafted with phosphonic acids of different hydrophobicitywere used as filler in poly(ethylacrylate) nanocomposites. Phosphonic acids bearing short alkyl chains ora diethylene glycol group have been grafted at densities up to 3.2 P/nm2 on NPs (20 nm) dispersed inwater. Nanocomposites at particle fractions up to 10 vol% have been formulated by casting from thecolloidal mixtures of modified NPs and nanolatex in water. The dispersion of the NPs in the polymermatrix has been studied by TEM combined with small-angle scattering, evidencing aggregation of NPs.TEM shows micrometer-scale inhomogeneities depending on the surface/polymer matrix compatibility.For the local interparticle correlations, a quantitative analysis of the intensity based on the mapping ontothe effective structure factor of polydisperse hard spheres is developed. This mapping allows the modelfreedetermination of the internal volume fraction of aggregates, termed compacity k, to between 10%and 30%, compatible with the TEM analysis. k is found to increase for the higher particle volume fractions,to decrease with grafting density, and to be mostly independent of the nature and mass of thegraft. Preliminary evidence for an improved compatibility of grafted with respect to bare NPs is found, asopposed to their aqueous precursor suspensions where some pre-aggregation is induced by grafting.

Polymer nanocomposites are used widely, mainly for the industrial application of car tyres. The rheological behavior of such nanocomposites depends in a crucial way on thedispersion of the hard filler particles – typically silica nanoparticles embedded in a soft polymer matrix. It is thus important to assess the filler structure, which may be quitedifficult for aggregates of nanoparticles of high polydispersity, and with strong interactions at high loading. This has been achieved recently using a coupled TEM/SAXSstructural model describing the filler microstructure of simplified industrial nanocomposites with grafted or ungrafted silica of high structural disorder. Here, wepresent an original method capable of reducing inter-aggregate interactions by swelling of nanocomposites, diluting the filler to low-volume fractions. Note that this isimpossible to reach by solid mixing due to the large differences in viscoelasticity between the composite and the pure polymer. By combining matrix crosslinking,swelling in a good monomer solvent, and post-polymerization of these monomers, it isshown that it is possible to separate the filler into small aggregates. The latter have then been characterized by electron microscopy and small-angle X-ray scattering,confirming the conclusions of the above mentioned TEM-SAXS structural model applied directly to the highly loaded cases.

Surface activity and micelle formation of alkylguanidinium chlorides, containing 10, 12, 14, and 16 carbon atoms in the hydrophobic tail have been studied by combining conductivity and surface tension measurements with isothermal titration calorimetry. The purity of the resulting surfactants, their temperatures of Cr → LC and LC → I transitions, as well as their propensity of forming birefringent phases were assessed based on the results of 1H and 13C NMR, differential scanning calorimetry (DSC), and polarizing microscopy studies. Whenever possible, the resulting values of Krafft temperature (TK), critical micelle concentration (CMC), minimum surface tension above the CMC, chloride counter-ion binding to the micelle, and the standard enthalpy of micelle formation per mole of surfactant (micH°), were compared to those characterizing alkyltrimethylammonium chlorides or bromides with the same tail lengths. The value of TK ranged between 292 and 314 K and increased strongly with increase in the chain length of the hydrophobic tail. Micellization was described as both entropy and enthalpy-driven. Based on the direct calorimetry measurements, the general trends in the CMC with the temperature, hydrophobic tail length and NaCl addition were found to be similar to those of other types of cationic surfactants. The particularly exothermic character of micellization was ascribed to the hydrogen-binding capacity of the guanidinium head-group.

Nanoparticles (NPs) can now be synthesized with a wide array of controlled sizes, shapes, and properties. However, turning them into nanomaterials often requires packing them into ordered assemblies to manifest specific electronic or optical properties for applications in nanoelectronics, optics, and metamaterials. Colloidal self-assembly (1) of NPs is relatively simple but is often restricted to high-symmetry crystals by the lack of specific directional bonds, especially for dilute NP solutions. To obtain lower symmetries that confer useful optical or electronic properties, long-range directional interactions must be imparted. On page 69 of this issue, Mundoor et al. (2) make clever use of an anisotropic host fluid, a liquid crystal, to promote the formation of a low-symmetry crystal in a dilute dispersion of nanorods.

The phenomenon of complexation between oppositely charged colloids or macromolecules in aqueous solution is a fundamental process, widely exploited by nature, as for example in DNA packaging within biological cells [2], but also by technology, as in industrial colloidal stabilization, water treatment and paper making [3].Being the result of a delicate balance of forces of different nature, small variations in the physico-chemical parameters may induce large changes in the resulting complexes [4]. Electrostatics is clearly the relevant interaction in driving the aggregation, although non-electrostatic interactions can be important in modulating the process and can deeply affect the characteristics of the resulting self-assembled structures. However, despite the intense experimental, theoretical and computational research aimed to understand the mechanisms driving the formation and the stabilization of the complexes [5], [6] and [7] in the physical context of macroion-multivalent counterion interactions [8], due to the great complexity of these systems, also the details of purely electrostatic interactions remain to be completely clarified.The possibility to get a fine control of the stability of the complexes by tuning the competition between attractive and repulsive electrostatic interactions justifies the actual enduring attention on polyion–colloid complexation, being key to the technological development of nano-structured materials or nano-devices to be used for example in drug delivery or gene-therapy [9] and [10].In particular, a rich literature exists on the variety of structures formed by charged liposomes interacting via electrostatic forces with oppositely charged linear polyions, whether they are synthetic polymers, polypeptides or DNA [11], [12] and [13]. A feature characterizing the phase behavior of these systems is the presence of a “reentrant condensation” accompanied by a marked “overcharging”, or charge inversion [14] and [15]. Indeed, when a given volume of a liposome suspension is mixed with the same volume of a solution containing oppositely charged polyelectrolytes, the complexation is systematically observed due to a rapid adsorption of polyelectrolytes chains at the liposome surface, forming what we have defined as “polyelectrolyte-decorated particles” (hereafter pd-particles), followed by their aggregation in pd–liposome clusters, as it is schematically represented in panel A of Fig. 1. For low enough polyelectrolyte concentration the clusters are small (they are formed by a few liposomes), after their rapid formation they are very stable, their measured ζ-potential being only slightly lower, in absolute value, than that measured for the liposomes in the absence of adsorbed polyelectrolytes. As the polyion concentration (and hence the ratio, ξ, between the number of stoichiometric charges on the polymer and on the particles) is increased, larger but still stable clusters are formed, with a ζ-potential which is further reduced in absolute value. At a sufficiently high polyelectrolyte concentration, the liposome suspension is completely destabilized, the large clusters that form are not stable, their ζ-potential is close to zero and they rapidly coalesce in macroscopic “flocs”. Going beyond the isoelectric point, hence further increasing the polyelectrolyte concentration, stable clusters form again, but now their size decreases upon increasing the polyelectrolyte concentration in the mixture: the polyelectrolyte-induced condensation of the liposomes is hence “reentrant”. At the same time, the ζ-potential after having passed through the zero, increases again in absolute value, and the sign of the excess charge of the clusters is that of the polyelectrolyte, i.e. opposite to that of the original liposomes (charge inversion).

Several techniques to assemble artificial lipid bilayers involve the zipping of monolayers. Theirefficiency is determined by the renewal of the saturated monolayers to be zipped and this proceeds byadsorption of lipids dispersed in oil as aggregates. The size of these lipids aggregates is a key parameterto ensure both the stability of the suspension and a fast release of lipids at the interface. We proposea new method inspired from the solvent-shifting nucleation process allowing to control and tune thelipid aggregates size and that improves the production of artificial membranes. It is simpler and fasterthan current methods starting from a dry lipid film, which are highly sensitive to environmental conditions.This method opens the route to bilayer production processes with new potentialities in membranecomposition.